It was/is mostly the same practice
except for the cases where it really counts. Window managers in general, xdotool, all kinds of input mapping and automation or the fact that you can write a screenshot tool in less than 500 LOC are only possible if you talk to X directly. And there the possibilities are almost limitless. And thanks to the xcb library it's actually somewhat convenient to use.
Also certain types of power tools for mac probably need use Quartz directly as well.